Coincidence of flood hydrograph can be generalized as mathematical constraints of date interval and magnitude for flood occurrence. A multivariate hydrological analysis model was developed to estimate the flood coincidence risk between the Yangtze and the Qing River. In this model, the mixed von Mises distribution was introduced to describe the interval, and a Copula function was adopted to establish a trivariate distribution of the 15-days flood volume and its interval for each river. By this model, a coincidence risk of 21. 9% was evaluated, the risk characteristics for different combinations of flood frequencies of the two rivers were analyzed. The results would provide a technical support to the united compensational operation of reservoirs on the Yangtze and the Qing River.
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